fix: auto-enable cluster bootstrap, add init-db.sql to postgres volumes

- Auto-enable cluster seeding when BOOTSTRAP_CLUSTERS is set
  (no longer requires separate BOOTSTRAP_ENABLE_CLUSTERS=true)
- Add BOOTSTRAP_ENABLE_CLUSTERS to README .env template
- Mount init-db.sql in postgres service volumes

README.md

@@ -75,7 +75,8 @@ BOOTSTRAP_REGISTRY_USER=admin-or-user
 BOOTSTRAP_REGISTRY_PASS=change-me
 BOOTSTRAP_REGISTRY_INSECURE=false
 
-# Kubernetes 集群 bootstrap，名称列表用逗号分隔
+# Kubernetes 集群 bootstrap，需要显式启用并设置名称列表
+BOOTSTRAP_ENABLE_CLUSTERS=true
 BOOTSTRAP_CLUSTERS=cluster1,cluster2
 BOOTSTRAP_CLUSTER_CLUSTER1_HOST=https://x.x.x.x:6443
 BOOTSTRAP_CLUSTER_CLUSTER1_DESC=GPU Cluster 1